This invention relates to ink jet systems utilizing pressure chambers and, more particularly, to a new and improved ink jet system having a pressure chamber arranged to inhibit formation of air bubbles therein.
In many ink jet systems, ink is supplied through a supply duct to a pressure chamber which communicates with an outlet orifice, and ink is ejected periodically from the orifice by a rapid contraction of the volume of the compression chamber as a result of action by an electromechanical transducer, such as a piezoelectric element. The rapid contraction is preceded or followed by a correspondingly rapid expansion of the chamber volume. During the expansion portion of the ink drop ejection cycle, the pressure of the ink in the pressure chamber is reduced significantly, increasing the tendency of any air dissolved in the ink within the chamber to form bubbles on the surface of the chamber. Bubbles tend to form in that manner especially at nucleation sites in the chamber such as sharp corners, minute cracks or pits, or foreign particles deposited on the chamber surface, where gases can be retained. Because the presence of gas bubbles within the pressure chamber prevents application of pressure to the ink in the desired manner to eject an ink drop of selected volume from the orifice at a selected time, it is important to avoid the formation of such bubbles in the pressure chamber of an ink jet system.
The Hara et al. U.S. Pat. No. 4,296,421 discloses an ink jet system using water-based or oil-based ink in which the pressure chamber and the discharge orifice are subjected to a treatment to make them water-repellent or oil-repellent so that they are not wetted by the ink used in the system, thereby making it possible to reduce the energy required to eject ink drops from the ink jet head. For this purpose, the orifice plate or the ink jet head is sprayed with a dispersion of Teflon or immersed in a toluene solution of a resin, such as silicone, epoxide, polyurethane, xylylene or the like which is not wetted by the ink used with the system.
The patent to Matsuzaki, U.S. Pat. No. 4,725,867, discloses a process for treating synthetic resin materials forming the ink passageways in an ink jet system to make them wettable by the ink used in the system so as to inhibit bubble formation. Since the treatment described in this patent does not change the surface of the materials, it does not eliminate nucleation sites, such as sharp corners, cracks, pits or foreign particles on the surface.